SEATTLE — In his second-floor office above a hair salon in north Seattle, Ryan Kunkel is seated on a couch placing $1,000 bricks of cash — dozens of them — in a rumpled brown paper bag. When he finishes, he stashes the money in the trunk of his BMW and sets off on an adrenalized drive downtown, darting through traffic and nervously checking to see if anyone is following him.

Despite the air of criminality, there is nothing illicit in what Mr. Kunkel is doing. He co-owns five medical marijuana dispensaries, and on this day he is heading to the Washington State Department of Revenue to commit the ultimate in law-abiding acts: paying taxes. After about 25 minutes at the agency, Mr. Kunkel emerges with a receipt for $51,321.

“Carrying such large amounts of cash is a terrible risk that freaks me out a bit because there is the fear in my mind that the next car pulling up beside me could be the crew that hijacks us,” he said. “So, we have to play this never-ending shell game of different cars, different routes, different dates and different times.”

Legal marijuana merchants like Mr. Kunkel — mainly medical marijuana outlets but also, starting this year, shops that sell recreational marijuana in Colorado and Washington — are grappling with a pressing predicament: Their businesses are conducted almost entirely in cash because it is exceedingly difficult for them to open and maintain bank accounts, and thus accept credit cards.

The problem underscores the patchwork nature of federal and state laws that have evolved fitfully as states have legalized some form of marijuana commerce. Though 20 states and the District of Columbia allow either medical or recreational marijuana use — with more likely to follow suit — the drug remains illegal under federal law. The Controlled Substances Act, enacted in 1970 classifies marijuana as a Schedule I drug, the most dangerous category, which also includes heroin, LSD and ecstasy.

As a result, banks, including state-chartered ones, are reluctant to provide traditional services to marijuana businesses. They fear that federal regulators and law enforcement authorities might punish them, with measures like large fines, for violating prohibitions on money-laundering, among other federal laws and regulations.

“Banking is the most urgent issue facing the legal cannabis industry today,” said Aaron Smith, executive director of the National Cannabis Industry Association in Washington, D.C. Saying legal marijuana sales in the United States could reach $3 billion this year, Mr. Smith added: “So much money floating around outside the banking system is not safe, and it is not in anyone’s interest. Federal law needs to be harmonized with state laws.”

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Mr. Kunkel and his business partner, Mr. Berman, left.CreditDavid Ryder for The New York Times

The limitations have created unique burdens for legal marijuana business owners. They pay employees with envelopes of cash. They haul Chipotle and Nordstrom bags containing thousands of dollars in $10 and $20 bills to supermarkets to buy money orders. When they are able to open bank accounts — often under false pretenses — many have taken to storing money in Tupperware containers filled with air fresheners to mask the smell of marijuana.

The all-cash nature of the business has also created huge security concerns for business owners. Many have installed panic buttons for workers in the event of a robbery and have set up a constellation of security cameras at their facilities beyond what is required, as well as floor sensors to detect break-ins. In Colorado, Blue Line Protection Group was formed a few months ago, specializing in protecting dispensaries and facilities that grow marijuana, and in providing transportation security. The firm largely uses military veterans who have Special Operations experience.

Marijuana business owners have devised strategies to avoid the suspicions of bankers. A number of legal operations have opened accounts by establishing holding companies with names that obscure the nature of their business. Some owners simply use personal bank accounts. Others have relied on local bank managers willing to take chances and bring them on as clients, or even offer tips on how to choose nondescript company names.

But the financial institutions eventually shut down many of these accounts after managers conclude the businesses are too much of a risk. It is not unusual for a legitimate marijuana business to go through a half-dozen bank accounts in a few years. While they are active, however, these accounts may have informal restrictions placed on them — some self-imposed — so they do not draw the scrutiny of bankers who may file suspicious-activity reports or would be required to report deposits over $10,000 in cash. The account holders may make only small deposits, and only at night and at certain branches. Mr. Kunkel of Seattle has such an account.

At the largest credit union in Washington State, BECU, about 20 accounts have been shut down in the last three years after it was discovered they were for businesses in the legal marijuana trade, Todd Pietzsch, a spokesman for the credit union, said.

Kristi Kelly, 36, who owns two dispensaries and several marijuana growing operations in the Denver area, said six bank accounts of hers had been canceled in the last 18 months. “Opening the account is not necessarily the problem,” she said. “Our cash deposit levels flag a bank’s compliance division.”

Ms. Kelly, who had just paid $10,000 in cash to the City of Denver for licensing and application fees to expand her business, said that several times a week she carried around tens of thousands of dollars in a bag. “I never felt as illegitimate as the day I had to buy a cash counter,” she said, adding that she spends three hours or so a day just managing the cash from her business’s multiple locations.

A.T.M.s are common in marijuana outlets, but the business owners often have to use their own cash in the machines in case law enforcement authorities conduct a raid and seize the money.

Those marijuana operations that do have bank accounts or use the personal ones of their owners can use a cashless A.T.M. service in which a debit card is swiped at a dispensary and the money is transferred into the recipient’s account.

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Mr. Kunkel, co-owner of five marijuana dispensaries, delivered a bag of cash to the Washington State Department of Revenue in Seattle. After 25 minutes, he emerged with a receipt for $51,321.CreditDavid Ryder for The New York Times

“It is operating over the A.T.M. network and not the credit card network,” said Lance Ott, whose company, Guardian Data Systems, provides this service. “The A.T.M. networks are not as regulated. This is the loophole.”

Since legal marijuana operations, for the most part, cannot get bank loans, these small businesses have to rely on short-term loans from individuals, usually with higher interest rates.

To help, High Times magazine is starting a private equity fund to invest in marijuana businesses. But many investors may feel uneasy about marijuana businesses that do not have bank accounts. And without bank references, entrepreneurs say, it is much tougher to get lines of credit from vendors.

Leaders in the marijuana trade point out that giving accounts to businesses would allow for more transparency and meticulous regulation and would help ensure that jurisdictions receive the taxes they are entitled to.

Marijuana entrepreneurs and banks both would like clear guidelines from the government on how financial institutions can serve the industry. On Friday, six members of Colorado’s congressional delegation sent a letter to the Treasury and the Justice Department requesting that they “expedite” that guidance.

In August, the Justice Department issued a memo indicating that it would not crack down on legal marijuana as long as eight regulatory requirements were met, like preventing revenue from the sale of marijuana from going to criminal enterprises and preventing the distribution of marijuana to minors. The memo did not address banking.

The Treasury Department’s Financial Crimes Enforcement Network hopes to circulate recommendations by the end of this month to officials at the Treasury and the Justice Department for their opinions, an official briefed on the situation said. There is no timetable for formal guidelines.

Richard Riese, senior vice president for regulatory compliance at the American Bankers Association, said banks wanted clear and comprehensive guidelines on how to do business with the legal marijuana industry.

Mr. Riese said, for instance, that banks would want to know that they were not “aiding and abetting” a criminal enterprise if they provided services to marijuana businesses. “Banks will need a lot of detail from regulators to get the satisfaction and comfort they are looking for,” he said.

Sheelagh McNeill contributed research.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Banks Say No to Marijuana Money, Legal or Not. Order Reprints | Today’s Paper | Subscribe

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